Baked Mushroom and Spinach Casserole

By , Test Kitchen Director · Reviewed by AislePrompt Editorial · ·

A creamy, savory casserole with mushrooms and spinach baked under a golden breadcrumb crust. This french-inspired vegetarian ready in about 50 minutes pairs sliced cremini mushrooms, butter, chopped onion for a weeknight-friendly dinner that comes together with one pan and minimal cleanup. Each serving lands at about 320 calories and feeds 6, so it slots cleanly into a weekly meal plan and pairs well with a quick salad or grain on the side. Tap "Plan a meal with the AI" below to drop this recipe into your week and send the ingredients straight to Instacart. Nutrition values are approximate, calculated from USDA FoodData Central (fdc.nal.usda.gov) — verify against ingredient labels for any health-driven dietary plan.

Prep: 20 min Cook: 30 min Serves 6 French cuisine 320 cal/serving
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Ingredients

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Instructions

  1. Step 1: Preheat oven to 375°F (190°C). Melt 2 tbsp butter in a large skillet over medium heat. Add 1/2 cup chopped onion and cook for 3-4 minutes until softened.
  2. Step 2: Add 10 oz sliced mushrooms and cook for 8-10 minutes until mushrooms release liquid and turn golden. Stir in 3 cups fresh spinach until wilted, about 2 minutes.
  3. Step 3: Remove from heat and stir in 1/2 cup heavy cream, 1/4 cup grated Parmesan, 1/4 tsp nutmeg, 1/2 tsp salt, and 1/4 tsp black pepper.
  4. Step 4: Transfer mixture to a 9x13 inch baking dish. Mix 1/4 cup panko breadcrumbs with 1 tbsp olive oil and sprinkle evenly over the top.
  5. Step 5: Bake for 25-30 minutes until topping is golden and casserole is bubbly around edges. Let rest 10 minutes before serving.

Frequently asked questions

How long does Baked Mushroom and Spinach Casserole take to make?

Total time is about 50 minutes (20 min prep + 30 min cook). Most home cooks find this fits comfortably into a weeknight; double the batch on Sunday for two dinners.

How do I store leftover Baked Mushroom and Spinach Casserole?

Cool to room temperature within 2 hours, then store in an airtight container in the fridge for up to 4 days. Reheat covered in a 350°F oven for 10-12 minutes, or microwave at 70% power in 60-second bursts to keep sliced cremini mushrooms from drying out.

Can I substitute ingredients in Baked Mushroom and Spinach Casserole?

Yes — most ingredients in this recipe have flexible swaps. For oil, use any neutral high-smoke-point oil (avocado, grapeseed, refined coconut). For aromatics, dried herbs at ⅓ the volume of fresh work in a pinch. The full ingredient list is shoppable on Instacart so you can see substitutes in real time.

How do I scale Baked Mushroom and Spinach Casserole for a different number of people?

The recipe is written for 6 servings. Multiply each ingredient by (your serving target / 6). Cook time stays roughly the same up to 2x; for 3-4x batches, switch from a skillet to a sheet pan or stockpot so the food isn't crowded — overcrowding steams instead of browns.

What goes well with Baked Mushroom and Spinach Casserole?

French vegetarian like this pair well with a simple grain (rice, couscous, or crusty bread), a quick salad with acid (lemon vinaigrette, pickled onions), and a pan sauce or yogurt-based dip. Tap "Plan a meal with the AI" to get specific side suggestions.

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